As illustrated in FIG. 13, a steering apparatus for an automobile is constructed such that the rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering unit 2, and as the input shaft 3 rotates, a pair of tie rods 4 are pushed and pulled, which applies a steering angle to the front wheels. The steering wheel 1 is supported by and fastened to the rear-end portion of a steering shaft 5, and that steering shaft 5 is inserted in the axial direction into a steering column 6 having a cylindrical shape, and is supported by the steering column 6 so as to be able to rotate freely. Moreover, the front-end portion of the steering shaft 5 is connected to the rear-end portion of an intermediate shaft 8 by way of a universal joint 7, and the front-end portion of the intermediate shaft 8 is connected to the input shaft 3 by way of another universal joint 9. In the construction illustrated in FIG. 13, an electric power steering apparatus is provided, and the front-end portion of the steering column 6 supports an electric motor 10 and is connected to a housing 11 that houses a reducer. Here, the forward-backward direction, the left-right direction (width direction) and the up-down direction, unless specified otherwise, refer to the forward-backward direction, left-right direction (width direction) and up-down direction of a vehicle body in which the tilt steering apparatus is installed.
In a steering apparatus for an automobile, a tilt mechanism to adjust the height position of the steering wheel 1 is normally assembled. A tilt steering apparatus, in which a manual tilt mechanism is installed, is constructed so as to be able to change between an adjustable state in which the height position of the steering wheel 1 is adjustable according to the operation of an adjustment lever (not illustrated), and a state in which the adjusted height of the steering wheel 1 is maintained. In this kind of tilt steering apparatus, a cam mechanism is assembled so as to improve the operational feeling of the adjustment lever, or a gear engaging means are installed in the tilt mechanism to strongly maintain the height position of the steering wheel 1.
Various kinds of construction are known for a tilt steering apparatus in which this kind of manual tilt mechanism is assembled, and FIG. 14 to FIG. 18 illustrate the construction as disclosed in JP 2012-040949 (A). This tilt steering apparatus has: a steering column 6a, a steering shaft 5a, a displacement-side bracket 12, a fixed-side bracket 13, an adjustment rod 14, a driven-side cam 15, a drive-side cam 16, an adjustment lever 17, a receiving bracket 18, a pivot arm 19, a pivot transmission portion 20, and buffer members 21a, 21b. 
In the illustrated construction, in addition to a tilt mechanism to adjust the height position of the steering wheel 1, a telescopic function to adjust the forward-backward position is also provided. In order to achieve this telescopic function, the steering column 6a is constructed such that the front portion of an inner column that is located on the rear side is fitted inside an outer column 22 that is located on the front side, so that the overall length of the steering column 6a can be expanded or contracted. The outer column 22 is formed into a U shape that is open on the top by bending metal plate, and restraining blocks 24 are fastened to the inside surfaces on the upper side of each. The front portion of the inner column 23 is fitted inside a portion that is surrounded by the restraining blocks 24 and the bottom surface of the outer column 22 so as to be able to be displaced in the axial direction. Moreover, the front-end portion of the outer column 22 is joined and connected to a housing 25 of a power steering apparatus in a state so as to protrude toward the rear from the housing 25. Furthermore, a support tube 26 is supported by and fastened to the front top portion of the housing 25, and the housing 25 and steering column 6a are supported by the vehicle body by way of a tilt shaft (not illustrated) that is inserted through the support tube 26 so as to be able to be pivotally displaced.
The steering shaft 5a is constructed by fitting the rear portion of the inner shaft 27, that is located in the front side, with the front portion of the outer shaft 28 that is located in the rear side by a spline fit so as to be able to transmit torque, and the steering shaft 5a expands or contracts as the steering column 6a expands or contracts. The steering shaft 5a is such that the rear-end portion protrudes toward the rear from the opening on the rear end of the steering column 6a, and supported on the inside of the steering column 6a so as to be able to rotate freely. In order for this, the portion near the rear end of the intermediate portion of the outer shaft 28 is supported on the inside of the rear-end portion of the inner column 23 by a bearing such as a single-row deep-groove ball bearing that supports radial loads and thrust loads. Moreover, the output shaft 29 of the power steering apparatus is joined and fastened to the front-end portion of the inner shaft 27 by way of a torsion bar, and the output shaft 29 is supported on the inside of the housing 25 by a similar ball bearing. The steering wheel 1 is fastened to the rear-end portion of the outer shaft 28.
The displacement-side bracket 12 is constructed by the upper section of a pair of left and right side plate portions 30 of the outer column 22, and the retaining block 24 that is fastened to the inside surface on the upper side of these side-plate portions 30. Through holes 32 for inserting the rod portion 31 of the adjustment rod 14 are formed in the portions in the side plate portions 30 and restraining block 24 that are aligned with each other.
The fixed-side bracket 13 is formed by bending using press working or by die cast molding of a metal such as a steel plate or an aluminum alloy, and has: an installation plate portion 33 for supporting and fastening the fixed-side bracket 13 to the vehicle body, and a pair of support plate portions 34a, 34b for supporting the displacement-side bracket 12 with respect to the fixed-side bracket 13. The pair of support plate portions 34a, 34b are provided so as to be parallel with each other in a state separated in the width direction and hanging down from the installation plate portion 33 so as to hold the displacement-side bracket 12 from both sides in the width direction. Vertically long holes 35a, 35b having a partial arc shape that is centered around the tilt shaft are formed in portions of the pair of support plate portions 34a, 34b that are aligned with each other.
The adjustment rod 14 is such that an outward-facing flange shaped anchor portion 37 is fastened to the base-end portion of the round rod shaped rod portion 31, and a male screw portion 38 is formed on the tip-end portion thereof. A convex engaging portion 39a that extends in the up-down direction is provided in a portion on the inside surface of the anchor portion 37 that surrounds the base-end portion of the rod portion 31. The convex engaging portion 39a is such that the width dimension in the forward-backward direction is slightly smaller than the width dimension in the forward-backward direction of the vertically long hole 35a that is provided in one of the support plate portions 34a, and the length dimension in the up-down direction is longer than the width dimension in the forward-backward direction of the vertically long hole 35a. The rod portion 31 of the adjustment rod 14 is inserted in the width direction through the vertically long holes 35a, 35b, and the through holes 32, and engages with the vertically long hole 35a of the one support plate portion 34a, and the inside surface of the anchor portion 37 comes in contact with the outside surface of the one support plate portion 34a. In this state, the male screw portion 38 of the rod portion 31 protrudes from the outside surface of the other support plate portion 34b. A buffer member 21a is fitted around the outside of the base-end portion of the rod portion 31. The buffer member 21a is made of synthetic resin and has a shape that covers both end surfaces on the top and bottom of the convex engaging portion 39a. In other words, a circular hole 40a for inserting the rod portion 31 through is provided in the center portion of the buffer member 21a, and buffer portions 41a are provided at both end portions on the top and bottom of the outside surface of the buffer member 21a. When the rod portion 31 is inserted through the circular hole 40a up to the base-end portion, both end surfaces of the top and bottom of the convex engaging portion 39a are covered by the top and bottom buffer portions 41a. 
The driven-side cam 15 is formed by forging a metal material such as an iron-based alloy or by performing the necessary finishing of a sintered metal that was obtained by powder metallurgy, so as to have the required strength, rigidity and resistance to wear, and a convex engaging portion 39b is provided on the inside surface, a driven-side cam surface 42 is provided on the outside surface, and a through hole 43a that passes through in the axial direction is provided in the center portion thereof. The convex engaging portion 39b, as in the case of the convex engaging portion 39a that is formed on the inside surface of the anchor portion 37, has a width dimension in the forward-backward direction that is slightly smaller than the width dimension in the forward-backward direction of the vertically long hole 35b that is provided in the other support plate portion 34b, and has a length dimension in the up-down direction that is larger than the width dimension in the forward-backward direction of the vertically long hole 35b. The buffer member 21b, as in the case of the buffer member 21a, has a circular hole 40b and a pair of buffer portions 41b, where in a state in which these buffer portions 41b cover both end surfaces on the top and bottom of the convex engaging portion 39b, being mounted to the inside surface of the driven-side cam 15, and being fitted around the outside of the portion near the tip end of the intermediate portion of the rod portion 31 of the adjustment rod 14. Moreover, the driven-side cam surface 42 is constructed such that an uneven surface is formed in the circumferential direction by making a convex portion, an inclined surface that is continuous in the circumferential direction with this convex portion, and a concave portion that is continuous in the circumferential direction of the inclined surface. Furthermore, the shape as seen from the axial direction of the through hole 43a is an elliptical shape. The tip-end portions of hook-shaped pieces 51 that protrude from both end portions in the width direction (forward-backward direction) of the center portions in the up-down direction of the outside surface of the buffer member 21b are engaged with the end edge portions of the driven-side cam surface 42 on both sides in the major axis direction of the through hole 43a, which prevents the driven-side cam 15 from coming apart from the buffer member 21b. 
The drive-side cam 16 is formed in the same way as the driven-side cam 15, with a drive-side cam surface 44 being provided on the inside surface thereof, and a circular through hole 43b that passes through in the axial direction being provided in the center portion thereof. The drive-side cam 16 is supported by the tip-end portion of the adjustment rod 14 in a state so as to be able to rotate centered around the adjustment rod 14, and such that displacement toward the tip-end side of the adjustment rod 14 is prevented. In order for this, a nut 45 is screwed onto the male screw portion 38 on the tip-end portion of the adjustment rod 14, and a thrust bearing 46 is placed between the inside surface of the nut 45 and the outside surface of the drive-side cam 16. The nut 45 is tightened to a specified torque, and then by crimping part (the outside end portion, for example) in the direction of the male screw portion 38, the nut 45 is prevented from becoming loose. By the drive-side cam surface 44 of the drive-side cam 16 engaging with the driven-side cam surface 42 of the driven-side cam 15, a cam apparatus 47 is formed that expands or contracts the dimension in the axial direction, or in other words, the distance in the axial direction between the outside surface of the drive-side cam 16 and the inside surface of the driven-side cam 15.
The adjustment lever 17 is formed by injection molding of synthetic resin that includes a high-function resin such as a polyamide or polyacetal, or is formed by die cast molding of a light alloy such as an aluminum alloy, and a concave holding portion 48 is provided in the base-end portion thereof. The drive-side cam 16 is held inside the concave holding portion 48 in a state in which relative rotation with respect to the concave holding portion 48 is prevented such that the adjustment lever 17 is able to rotate and drive the drive-side cam 16. An opening portion is provided in the bottom portion of the concave holding portion 48, which allows the outside surface of the drive-side cam 16 to come in direct contact with the thrust bearing 46. Therefore, the drive-side cam 16 and the base-end portion of the adjustment lever 17, and the adjustment rod 14 and the nut 45 are capable of relative rotation.
The receiving bracket 18 is formed using a metal material that is able to maintain sufficient strength and rigidity, and being separated from the fixed-side bracket 13, is supported and fastened to the outside surface of the other support plate portion 34b by screws or the like. The receiving bracket 18 is open in the front and in both the top and bottom ends, and has a concave groove 49 that extends in a direction along the vertically long hole 35b. The concave groove 49 is formed into a V shape such that the width at the opening portion is wide, and is inclined becoming narrower going toward the bottom. A female gear 50, which has a rack tooth shape with respect to the up-down direction, is provided on the inside surface of both sides of the concave groove 49.
The pivot arm 19 is supported around the driven-side cam 15 such that relative rotation and a small amount of relative displacement in at least the up-down direction with respect to the driven-side cam 15 is possible. In order for this, a support hole 52 having an inner diameter that is slightly larger than the outer diameter of the driven-side cam 15 is provided on the base-end portion of the pivot arm 19. With the driven-side cam 15 located inside the support hole 52, a centering spring 53 is provided between the driven-side cam 15 and the base-end portion of the pivot arm 19. In a state in which there is no external force acting on the driven-side cam 15, the driven-side cam 15 is located in the center position in the up-down direction inside the support hole 52 due to the elastic force of the centering spring 53. A male gear 54 that can engage or disengage with the female gear 50 on the inside surface of the concave groove 49 is provided on both side surfaces of the tip-end portion of the pivot arm 19. The cross-sectional shape of the tip-end portion of the pivot arm 19 is a wedge shape, the thickness dimension of which becomes smaller going toward the tip edge of the portion where the male gear 54 is formed.
The pivot transmission portion 20 is provided between the adjustment lever 17 and the pivot arm 19 so as to rotate the pivot arm 19 centered around the adjustment rod 14 together with the adjustment lever 17. Specifically, a protrusion 55 that is formed in the portion near the tip end of the outside surface of the pivot arm 19 is caused to gently engage with an concave engaging portion that is formed in the inside surface of part of the adjustment lever 17. As a result, in a state in which the adjustment lever 17 is rotated upward and the dimension in the axial direction of the cam apparatus 47 is expanded, the female gear 50 and male gear 54 engage with each other, however, when in the state in which the adjustment lever 17 is rotated downward and the dimension in the axial dimension of the cam apparatus 47 is contracted, the female gear 50 and male gear 54 become disengaged.
In this kind of tilt steering apparatus, when adjusting the height position of the steering wheel 1, the adjustment lever 17 is rotated downward, which causes the convex portions of the drive-side cam surface 44 of the drive-side cam 16 of the cam apparatus 47 to face the concave portions of the driven-side cam surface 42 of the driven-side cam 15, and the dimension in the axial direction of the cam apparatus 47 is contracted. In this state, the surface pressure at the contact areas between the inside surfaces of the support plate portions 34a, 34b of the fixed-side bracket 13 and the outside surface of the outer column 22 of the steering column 6a is decreased or lost. Moreover, the female gear 50 and the male gear 54 become disengaged. Therefore, the height position of the steering wheel 1 is adjusted within the range in which the buffer members 21a, 21b can be displaced inside the vertically long holes 35a, 35b. During this adjustment work, when the steering wheel 1 is moved to the top-end position or bottom-end position of the adjustable range, the buffer portions 41a, 41b of the buffer members 21a, 21b that are made of synthetic resin come in contact with the top-end portion or bottom-end portion of the peripheral edge of the vertically long holes 35a, 35b. As a result, the occurrence of an impact or noise that is unpleasant for the driver that is operating the steering wheel 1 due to the impact between metal members is prevented. Moreover, in the example in the figures, when the dimension in the axial direction of the cam apparatus 47 is contracted, the surface pressure of the engaging portion between the outer column 22 and the inner column 23 is also decreased or lost, so by moving the inner column in the forward-backward direction, it is also possible to adjust the forward-backward position of the steering wheel 1.
After the steering wheel 1 has been moved to a desired position, the adjustment lever 17 is rotated upward, which causes the convex portions of the drive-side cam surface 44 and the driven-side cam surface 42 to come face to face with each other, and the dimension in the axial direction of the cam apparatus 47 expands. In this state, the surface pressure at the contact areas between the inside surfaces of the support plate portions 34a, 34b and the outside surface of the outer column 22 increases, and at the same time the surface pressure at the fitting portion between the outer column 22 and the inner column 23 also increases. Moreover, the female gear 50 and the male gear 54 engage. When the steering wheel 1 is moved to a desired position, and the adjustment lever 17 is simply rotated upward does not absolutely mean that female gear 50 and the male gear 54 will engage. In this case as well, the pivot arm 19 on which the male gear 54 is provided is displaced in the up-down direction with respect to the driven-side cam 15 while causing the centering spring 53 to elastically deform, which causes the female gear 50 and the male gear 54 to engage. As a result, the steering wheel 1 is maintained at the adjusted position. Even in the case of a secondary impact in which a large force is applied in a direction that causes the steering wheel 1 to rise, the large maintaining force due to the engagement between the female gear 50 and the male gear 54 prevents the steering wheel 1 from jumping up.
In the example in the figure, an elastic locking piece 57 that engages with a locking stepped portion 56 that is formed on the receiving bracket 18 when the adjustment lever is rotated upward is provided at the base-end portion of the adjustment lever 17. A sleeve 58 is provided inside the through hole 43b that is in the center of the drive-side cam 16. An energy absorbing member 59 is provided on the top surface of the inner column 23. FIG. 19 illustrates construction that is disclosed in WO 2012/011424 (A1), however, in this construction, part of the pivot arm 19 is covered by a first buffer plate 60 and a second buffer plate 61 made of synthetic resin.
In the case of this kind of tilt steering apparatus, the buffer members 21a, 21b lessen the impact that occurs when the top-end surfaces or bottom-end surfaces of the convex engaging portions 39a, 39b collide with the top-end surfaces or bottom-end surface of the peripheral edges of the vertically long holes 35a, 35b during up-down position adjustment of the steering wheel 1. The buffer portions 41a, 41b of the buffer members 21a, 21b cover both the top and bottom end surfaces of the convex engaging portions 39a, 39b, however, the center portion in the up-down direction of both side surfaces in the forward-backward direction of the convex engaging portions 39a, 39b are not recessed more than the buffer portions 41a, 41b and are exposed.
On the other hand, as illustrated in FIG. 20, minute gaps for allowing the convex engaging portions 39a, 39b and buffer members 21a, 21b to move smoothly along the vertically long holes 35a, 35b are provided between the front-side edge 62 and rear-side edge 63 of the vertically long holes 35a, 35b, and both side surfaces in the front and rear of the convex engaging portions 39a, 39b and both side surfaces in the front and rear of the buffer members 21a, 21b. Therefore, the convex engaging portions 39a, 39b and buffer members 21a, 21b can rotate centered around the adjustment rod 14 inside the vertically long holes 35a, 35b just the amount of the minute gaps. Therefore, when the drive-side cam 16 is rotated by the adjustment lever 17 in the tightening direction (direction that expands the dimension in the axial direction of the cam apparatus 47) after the position of the steering wheel 1 has been adjusted, the driven-side cam 15 having convex engaging portions 39b on the inside surface thereof also rotates in the same direction just the amount of the minute gap. Similarly, when the adjustment lever 17 is rotated in the opposite direction of the tightening direction, the driven-side cam 15 rotates in the same direction just the amount of this minute gap.
The vertically long holes 35a, 35b have a partial arc shape that is centered around the tilt shaft, so the front-side edges 62 of the peripheral edges of the vertically long holes 35a, 35b are convex arcs, and the rear-side edges 63 are concave arcs. Therefore, when the convex engaging portions 39a, 39b are pivotally displaced inside the vertically long holes 35a, 35b centered around the adjustment rod 14, there is a collision of the metal of the portions near both ends in the up-down direction of the side surfaces on the front side of the convex engaging portions 39a, 39b, and the front-side edges 62 of the vertically long holes 35a, 35b. Particularly, with regard to the convex engaging portion 39b that is formed on the inside surface of the driven-side cam 15, the amount of this collision can easily become severe. The reason for this is that due to the engagement between the inclined surfaces of the driven-side cam surface 42 and the drive-side cam surface 44 during the process of operating the adjustment lever 17, regardless of the intention of the driver that operates the adjustment lever 17, it is easy for the adjustment lever to rotate with much energy.
However, it is feasible to simply cause both end portions in the front and rear of the buffer portion 41b of the buffer member 21b to protrude toward the front and rear further than both side surfaces in the front and rear of the convex engaging portion 39b, such that only both end portions in the front and rear of the buffer portion 41b will come in contact with the edges 62, 63 on both the front and rear sides of the vertically long hole 35b in a pre-loaded state. In this construction, looseness in the direction of rotation between the convex engaging portions 39b and the buffer member 21b is eliminated, so the driver that operates the adjustment lever 17 does not experience a feeling of looseness, and it is possible to prevent collision between metal members. However, in this construction, the friction force that acts on the contact areas between the edges 62, 63 on both the front and rear sides of the vertically long hole 35b and both end portions in the front and rear of the buffer portion 41b becomes large. This friction force has an adverse effect on the smooth operation of adjustment of the height position of the steering wheel 1.
Moreover, in the case of this construction, it is difficult to sufficiently maintain durability of the buffer portion 41b. In other words, in a state in which only the buffer portion 41b comes in contact with the edges 62, 63 on both the front and rear sides of the vertically long hole 35b, a rotation force is applied to the buffer portion 41b from the convex engaging portion 39b in the tightening direction of the drive-side cam 16. The rotation force is applied to the buffer portion 41b by way of the engaging portion between both end surfaces on the top and bottom of the convex engaging portion 39b, and the end surfaces of the buffer portion 41b, which is the opposing surfaces, that face each other. However, the end surfaces of the buffer portion 41b that face each other are surfaces that do not have any stepped portion, and they face approximately in the up-down direction. In other words, the end surfaces of the buffer portion 41b that face each other, face in a direction so as not to be able to efficiently support the rotation force in the tightening direction of the drive-side cam 16 (force in the circumferential direction centered around the adjustment rod 14). Therefore, there is a possibility that this rotation force will damage the buffer portion 41b, or that the shock absorbing function of the buffer portion 41b will be lost.
In addition, JP 2008-307959 (A) discloses construction of a driven-side cam in which the cam surface portion is formed using a metal material, and the convex engaging portion are made of synthetic resin. With this construction, it is possible to prevent the occurrence of noise that is caused by contact between metal of the driven-side cam and the support plate portions. However, the entire convex engaging portions of the driven-side cam that engages with the vertically long holes are made of just synthetic resin, so as the edges on both the front and rear sides of the convex engaging portions are used over a long period of time, the wear gradually becomes large due to sliding contact with the edges on both the front and rear sides of the vertically long holes and the looseness becomes large. Furthermore, it is possible to form the vertically long holes so as to be straight, however, this is not preferred because it becomes impossible to smoothly adjust the up-down position of the steering wheel 1.